Explanation

For an adiabatic process (insulated container), $T_2/T_1 = V_2/V_1$. Thus, $T_2 = 5 imes 500 K / 3 = 833.3 K$ is incorrect. The correct formula for this specific case using $ ext{C}_p$ and the work done or internal energy change leads to $T_2 = 274 K$.